Currently, by introducing a portion of technology that had been considered for fourth generation systems to the third generation frequency band, the EUTRA (Evolved Universal Terrestrial Radio Access) that aims for an improvement of transmission speed is being studied by the standards group 3GPP (3rd Generation Partnership Project) (refer to Non-Patent Document 1 and Non-Patent Document 2).
The adoption of the OFDMA (Orthogonal Frequency Division Multiplexing Access) system that as a transmission method is resistant to multi-pass interference and suitable for high-speed transmission has been decided in EUTRA. Also, in the detailed specifications relating to upper layer operation such as the data transfer control and resource management control of EUTRA, low delay and low overhead have been achieved, and moreover adoption of the simplest possible technology is being advanced (Non-Patent Document 2).
Regarding the control system when downlink synchronization loss is detected in the lower layer among the control of the upper layer in EUTRA, a control method that is approximately the same as W-CDMA (Wideband-Code Division Multiple Access) that was adopted in the third generation mobile radio access network UTRAN (Universal Terrestrial Radio Access Network) is being considered (refer to Section 10.1.6 in Non-Patent Document 2). In the W-CDMA method, in a mobile station device that detects downlink synchronization loss, control that stops uplink data is necessary (refer to section 6.4.4 of Non-Patent Document 3). The information that a mobile station device transmits to a base station device due to a radio resource request or closed loop control by the abovementioned control (for example, quality information index or packet resending control information, and electric power control information) is, when downlink synchronization is lost, not notified to the base station device, and so closed loop control is not achieved, and there is the possibility of wasting radio resources power consumption. For that reason, many methods that do not cause downlink synchronization loss in W-CDMA have been proposed (Patent Document 1).
FIG. 20 is a figure for explaining the process of transmission of a mobile station device to the base station device (FIG. 20 (a)), and subsequent reception in the conventional technology (FIG. 20 (b)). The mobile station device judges the downlink synchronization state using any of the downlink channels during reception.
FIG. 20 shows the state transition of the uplink channel and the downlink channel in the case of transitioning to the idle state (the state in which the mobile station device and the base station device are not wirelessly connected) after detection of a downlink channel error and both recovery of downlink synchronization and reconnection not being possible. Here, in the case of a downlink synchronization error being detected in the downlink channel, since the mobile station device judges whether or not the downlink synchronization error is temporary, the downlink channel state is made to transition from the synchronized interval P11 to the error detection interval P12.
Moreover, in the case of a downlink synchronization error being continuously detected even in the error detection interval P12, and downlink synchronization errors of a definite number of times being detected, next a transition is made to the synchronization protection interval P13 that attempts to recover the downlink synchronization state and simultaneously starts a timer that times the synchronization protection interval P13.
At this time, the mobile station device stops transmission of the signal using the uplink channel from a mobile station device to the base station device. This interval is called the data signal transmission stop interval 21. Even if the synchronization of the downlink channel has not recovered by the time of measurement by the timer having expired, it makes the judgment of having reached downlink synchronization loss, and the mobile station device transitions to a reconnection interval P14 attempts reconnection, and simultaneously starts a timer that times the reconnection interval P14. In the reconnection interval P14, the mobile station device repeatedly performs the cell reselection procedure that selects a cell of good quality. The mobile station device that chose a good cell with the cell reselection procedure performs a reconnection request to the aforementioned cell using an asynchronous random access channel. When permission to the reconnection request is not issued from the base station device until the timing by the timer expires, the mobile station device judges that reconnection as having failed and releases the radio resources, and transitions to an idle state interval P15 in which radio connection is not performed to the base station device.
FIG. 21 is a figure for explaining the process of the transmission of a mobile station device to a base station device (FIG. 21 (a)), and subsequent reception (FIG. 21 (b)) in the conventional technology. FIG. 21 shows the state transition of the uplink channel and the downlink channel in the case of, following a downlink synchronization error detection in the downlink channel, the downlink synchronization having recovered before downlink synchronization loss. It is the same as FIG. 20 up until the state of the downlink channel transitioning to the synchronization protection interval P13, and the uplink channel state becoming the uplink channel stop interval P21.
Here, in the case of the synchronization of the downlink channel having recovered before the timing by the above-mentioned timer having expired, the mobile station device transitions the downlink channel state to the synchronous interval P16, and resumes transmission of the uplink data channel to return to the normal state.
FIG. 22 is a figure for explaining the process of the transmission of a mobile station device to a base station device (FIG. 22 (a)) and the subsequent reception (FIG. 22 (b)) in the conventional technology.
FIG. 22 shows the state transition of the uplink channel and the downlink channel in the case of, following a downlink synchronization error detection in the downlink channel, reconnection being made. It is the same as FIG. 20 up until performing a reconnection request to the base station device of the cell selected by the cell reselection procedure, after downlink synchronization loss occurs. Here, when a reconnection permission is issued from the base station device prior to the timing by the timer expiring, the downlink channel state is transitioned to the synchronization establishment interval P17 that attempts synchronization with the selected cell, and after synchronization is achieved, the downlink channel state is transitioned to synchronization interval P16, and simultaneously the transmission of the uplink data channel that had been stopped is resumed to return to the normal state.
FIG. 23 is a sequence diagram that shows the process of a mobile communication system in the conventional technology. FIG. 23 shows an example of the adjustment method of the uplink transmission timing when the state of the uplink channel of a mobile station device in EUTRA is uplink asynchronous. Since the mobile station device has not achieved uplink synchronization, it is transmitting preamble data by an asynchronous random access channel, and so the uplink transmission timing is adjusted from the base station device. The base station device receives a signal transmitted by the asynchronous random access channel from the mobile station device (Step S11), and measures the timing discrepancy between the reception timing and subframe lead position of the base station device (Step S12). The timing discrepancy is notified to a mobile station device as uplink timing adjustment control data (Step S13). Even if the downlink channel that issues the uplink timing adjustment control data is a downlink data channel, it may be a downlink common control channel.
A mobile station device adjusts the uplink transmission timing according to the issued uplink timing adjustment control data (Step S14), and uses it as uplink transmission timing of subsequent uplink data (Step S15).
FIG. 24 is a sequence diagram that shows the process of a mobile communication system in the conventional technology. FIG. 24 shows another example of the adjustment method of the uplink transmission timing when the state of the uplink channel of a mobile station device in EUTRA is in synchronization. The base station device receives the uplink data that is transmitted at least once within a predetermined cycle from a mobile station device (Steps S21, S25), and measures the timing discrepancy between the reception timing and the subframe lead position of the base station device (Steps S22, S26). The timing discrepancy is notified to the mobile station device at least once within a predetermined cycle as uplink timing adjustment control data (Steps S23, S27).
The base station device uses data of any uplink channel as uplink data transmitted from the above-mentioned mobile station device that is used in order to measure the timing discrepancy.
A mobile station device adjusts the uplink transmission timing according to the uplink timing adjustment control data that has been issued (Steps S24, S28), and uses it as uplink transmission timing of subsequent uplink data. Here, when the time during which uplink synchronization between the base station device and the mobile station device can be continued, that is, the time that guarantees that uplink synchronization is maintained assuming a normal transmission state, serves as the uplink synchronization adjustment cycle, the uplink timing adjustment control data must be transmitted to the mobile station device one within the uplink synchronization adjustment cycle. Also, the uplink data must be transmitted to the base station device one within the uplink synchronization adjustment cycle. When the uplink data is not transmitted even once within the uplink synchronization adjustment cycle due to intermittent reception or the like, the uplink synchronization state is judged to be asynchronous.
FIG. 25 is a sequence diagram that shows the process of a mobile communication system in the conventional technology. FIG. 25 shows the transition of the downlink synchronization state in both of the mobile station device and the base station device during the occurrence of downlink synchronization loss and related radio controls. The process of FIG. 25 starts from the state of the synchronization intervals P11, P31 in which the mobile station device and the base station device perform mutual communication.
Due to reasons of quality degradation of the downlink channel, the downlink synchronization state of the mobile station device side transitions to the error detection interval P12, and moreover when the error detection interval P12 ends as is without the downlink synchronization recovering, the downlink synchronization state of the mobile station device side transitions to the synchronization protection interval P13, and the transmission portion of the mobile station device performs uplink transmission stop control as a result of being notified of the transition to the synchronization protection interval P13 (Step S32).
Furthermore, even if the synchronization protection interval P13 ends, when the downlink synchronization does not recover, the downlink synchronization state of the mobile station device side transitions to the reconnection interval P14, and in the radio portion of the mobile station device, by the detection of downlink synchronization loss being notified (Step S33), cell reselection control is started (Step S34). In the event of a suitable cell being detected by the cell reselection control, the occurrence of cell reselection is notified to the base station device using a random access channel (Steps S35, S36). The base station device first causes the synchronization state of the base station device to transition from the synchronization interval P31 to the reconnection interval P32 upon receiving a signal of the random access channel, and performs downlink transmission stop control (Steps S37, S38).
Patent Document 1: PCT (WO) 2003-524987
Non-Patent Document 1: 3GPP TR (Technical Report) 25.814, V1.5.0 (2006-5), “Physical Layer Aspects for Evolved UTRA”. [URL: http://www.3gpp.org/ftp/Specs/html-info/25814.htm]
Non-Patent Document 2: 3GPP TS (Technical Specification) 36.300,V0.4.0 (2007-1), “Overall description; Stage2”. [URL: http://www.3gpp.org/ftp/Specs/html-info/36300.htm]
Non-Patent Document 3: 3GPP TS (Technical Specification) 25.101,V7.5.0 (2006-9), “User Equipment (UE) radio transmission and reception (FDD)”. [URL: http://www.3gpp.org/ftp/Specs/html-info/25101.htm]
However, in the conventional technology, as shown in FIG. 25, in the interval until informing the occurrence of a cell reselection to the base station device after the mobile station device transitions to the error detection interval P12, a disagreement in the downlink synchronization state of the mobile station device and the base station device occurs. For that reason, the disagreement interval of this downlink synchronization state is scheduled, and so there is a possibility that the downlink data that is transmitted from the base station device to the mobile station device will not be received, giving rise to the problems of the radio resources being wastefully consumed and the radio utilization efficiency falling.
When a downlink synchronization error occurs in a mobile station device in connection with this, there has been the problem of time being required until being able to perform communication in a state of the communication quality being good between the base station device and the mobile station device.
The present invention was achieved in view of the above circumstances, and has as its object to provide a mobile communication system, a mobile station device, a base station device, and a mobile communication method that are capable of performing communication in a state of the communication quality being good between the base station device and the mobile station device even in the case of a downlink synchronization error occurring at the mobile station device.